Apparatus and method for preventing etch chamber contamination

ABSTRACT

An apparatus and a method for preventing particle contamination in a plasma etch chamber equipped with a middle chamber by residual etchant gas is provided. In the apparatus, a bypass exhaust conduit is provided for connecting between a middle chamber cavity and a main chamber cavity such that when a pump means is turned on to evacuate the main chamber cavity, any residual etchant gas in the middle chamber cavity can be rapidly evacuated without the danger of causing metal corrosion in the middle chamber cavity. Any chamber contamination caused by the metal corrosion can thus be avoided.

FIELD OF THE INVENTION

[0001] The present invention generally relates to an apparatus and amethod for operating and etch chamber with reduced contamination andmore particularly, relates to an apparatus and a method for preventingresidual etchant gas in the middle chamber of an etch chamber fromattacking metal sidewalls of the middle chamber by providing a bypassexhaust conduit to evacuate any residual etchant gas.

BACKGROUND OF THE INVENTION

[0002] In the fabrication of semiconductor devices, particularly in thefabrication of sub-micron scale semiconductor devices, profiles obtainedin etching process are very important. A careful control of a surfaceetch process is therefore necessary to ensure directional etching. Inconducting an etching process, when an etch rate is considerably higherin one direction than in the other directions, the process is calledanisotropic. A reactive ion etching (RIE) process assisted by plasma isfrequently used in an anisotropic etching of various material layers ontop of semiconductor substrate. In plasma enhanced etching processes,the etch rate of a semiconductor material is frequently larger than thesum of the individual etch rates for ion sputtering and individualetching due to a synergy in which chemical etching is enhanced by ionbombardment.

[0003] To avoid subjecting a semiconductor waiver to high-energy ionbombardment, the wafer may also be placed downstream from the plasma andoutside the discharge area. Downstream plasma reactors etches more in anisotropic manner since there are no ions to induce directional etching.The downstream reactors are frequently used for removing resist or otherlayers of material where patterning is not critical. In a downstreamreactor, radio frequency may be used to generate long-lived activespecies for transporting to a wafer surface relocated remote from theplasma. Temperature control problems and radiation damage are thereforesignificantly reduced in a downstream reactor. Furthermore, the waferholder can be heated to a precise temperature to increase the chemicalreaction rate, independent of the plasma.

[0004] In a downstream reactor, an electrostatic wafer holding deviceknown as an electrostatic chuck is frequently used. The electrostaticchuck attracts and holds a wafer positioned on top electrostatically.The electrostatic chuck method for holding a wafer is highly desirablein the vacuum handling and processing of wafers. An electrostatic chuckdevice can hold and move wafers with a force equivalent to several tensof Torr pressure, in contrast to a conventional method of holding wafersby a mechanical clamping method.

[0005] Referring initially to FIG. 1, wherein a conventional inductivelycoupled plasma etched chamber 10 is shown. In the etch chamber 10, whichtypically represents one that is commercially available as a LAM TCPetcher, the plasma source is a transformer-coupled source that generatesa high density, low pressure plasma away from a wafer surface. Theplasma source allows an independent control of ion flux and ion energy.The plasma can be generated by a flat spiral coil (not shown), i.e. aninductive coil separated from the plasma by a dielectric plate 12 whichis normally fabricated of a ceramic material with a gas inlet 14provided therein. The ceramic plate 12 may be a dielectric window madeof a substantially transparent material such as quartz to facilitatevisual observation of the middle chamber 20. The middle chamber 20 isfurther formed by a bottom ceramic plate 16 equipped with an aperturedopening 18 for allowing a plasma to pass thereto. The sidewall 22 of themiddle chamber 20 is normally formed of a metallic material, such asaluminum, with an anodized aluminum surface. The top ceramic plate 12,the bottom ceramic plate 16 and the metallic sidewall 22 form aself-contained chamber, i.e. the middle chamber 20 which has a firstcavity 24 therein.

[0006] A wafer 30 is positioned on the electrostatic chuck (or ESC) 26sufficiently away from the RF coil (not shown) such that it is notaffected by the electromagnetic field generated by the RF coil. Atypical LAM TCP plasma etcher enables a high density plasma to beproduced and a high etch rate to be achieved. In the plasma etcher 10,an inductive supply and a bias supply are further used to generate thenecessary plasma field. In a typical inductively coupled RF plasmaetcher 10, shown in FIG. 1, a source frequency of 13.5 MHZ and asubstrate bias frequency of 13.5 MHZ are utilized such that ion densityof about 0.5˜2.0×10¹² cm³ is obtained at the wafer level, while electrontemperature of 3.5˜6.0 eV and a chamber pressure of 1˜25 mTorr areachieved.

[0007] In the plasma chamber 10, after the wafer 30 is etched in themain chamber 32, the chamber is normally evacuated of the etchant gasfrom the middle chamber 20 and from the main chamber 32 by a turbo pump34 controlled by a gate valve 36. The turbo pump is further connected toa dry pump 38 through a control valve 42. When the pressure in thechamber is too high, in order not to damage the turbo pump 34, controlvalve 42 closes while control valve 44 opens to allow the chamber to beevacuated by the dry pump 38 directly. Simultaneous with the pumpingprocess, an inert purge gas such as nitrogen is flown into the middlechamber 20 and the main chamber 32 through gas inlet 14 to furtherfacilitate the removal of residual etchant gas.

[0008] In the conventional plasma chamber 10, a problem caused by theresidual etchant gas left in the cavity 24 of the middle chamber 20frequently occurs. The residual etchant gas cannot be evacuated fromcavity 24 due to the small holes in the apertured opening 18 situated inthe bottom ceramic plate 16. The small holes do not allow a fast flowrate so that the evacuation of the middle chamber 20 is ineffective. Theresidual etchant gas left in cavity 24 attacks the metal sidewall 22 andthus causing corrosion in the metal. The corrosion of metal, forinstance of an aluminum surface, produces particles which contribute toa severe contamination problem for the main chamber 32 where a wafer ispositioned.

[0009] It is therefore an object of the present invention to provide aplasma etch chamber that does not have the drawbacks or shortcomings ofa conventional plasma etch chamber.

[0010] It is another object of the present invention to provide a plasmaetch chamber that is equipped with a middle chamber that hassignificantly reduced particle contamination problem.

[0011] It is a further object of the present invention to provide aplasma etch chamber that is equipped with a middle chamber and a mainchamber which has significantly reduced contamination problem byevacuating residual etchant gas from the middle chamber.

[0012] It is another further object of the present invention to providea plasma etch chamber that is equipped with a middle chamber for feedingan etchant gas plasma into a main chamber that has significantly reducedparticle contamination problem.

[0013] It is still another object of the present invention to provide aplasma etch chamber that has a middle chamber and a main chamberequipped with a bypass exhaust conduit connecting the middle chamber tothe main chamber.

[0014] It is yet another object of the present invention to provide aplasma etch chamber that has a middle chamber and a main chamber influid communication through an apertured opening and a bypass exhaustconduit.

[0015] It is still another further object of the present invention toprovide a method for preventing corrosion in an etch chamber by residualetchant gas wherein the etch chamber is equipped with a middle chamberand a main chamber.

[0016] It is yet another further object of the present invention toprovide a method for preventing particle contamination in an etchchamber by providing a bypass exhaust conduit connecting between amiddle chamber and a main chamber such that residual etchant gas can beevacuated from the middle chamber.

SUMMARY OF THE INVENTION

[0017] In accordance with the present invention, an apparatus and amethod for preventing particle contamination in an etch chamber areprovided.

[0018] In a preferred embodiment, a plasma etch chamber is providedwhich includes a main chamber that has a first cavity, a wafer platformand a spent etchant gas outlet in fluid communication with a pump meansfor exhausting a spent etchant gas; a middle chamber that has a secondcavity therein situated inside the first cavity and suspended over thewafer platform; the middle chamber is formed by a top ceramic plate, abottom ceramic plate and a metal sidewall; the second cavity is in fluidcommunication with the first cavity through an apertured openingsituated in the bottom ceramic plate for feeding an exhaust gas plasmainto the first cavity; the second cavity is in fluid communication withan etchant gas source through an etchant gas inlet situated in the topceramic plate; and a bypass exhaust conduit providing fluidcommunication between the second cavity in the middle chamber through anopening in the top ceramic plate and the first cavity in the mainchamber such that any residual etchant gas in the second cavity isevacuated by the pump means through the first cavity without causingcorrosion in the metal sidewall of the middle chamber.

[0019] In the plasma etched chamber, the main chamber may have a volumethat is at least twice the volume of the second cavity in the middlechamber. The wafer platform may be an electrostatic chuck. The aperturedopening in the bottom ceramic plate may be a shower head for dispersingan etchant gas plasma into the first cavity of the main chamber. Thebypass exhaust conduit allows the residual etchant gas to flowtherethrough at a flow rate at least twice the flow rate of the residualetchant gas flown through the apertured opening in the bottom ceramicplate. The spent etchant gas outlet may be in fluid communication with aturbo pump, or maybe in fluid communication through a gate valve forcontrolling a passageway of the spent etchant gas, the top ceramic plateand the bottom ceramic plate may be formed of a ceramic material that isresistant to the etchant gas plasma. The metal sidewalls of the middlechamber may be formed of aluminum. The etchant gas plasma may be formedof at least one member selected from the group consisting of Cl₂ or BCl₃in the middle chamber by a radio frequency coil.

[0020] The present invention is further directed to a method forpreventing corrosion in an etch chamber by residual etchant gas whichcan be carried out by the operating steps of first providing an etchchamber that includes a main chamber and a middle chamber, the mainchamber further includes a first cavity and a wafer platform with themiddle chamber suspended over the wafer platform, the middle chamberfurther includes a top ceramic plate that has an etchant gas inlettherethrough, a bottom ceramic plate that has an apertured opening forpassing an etchant gas plasma therethrough and metal sidewalls defininga second cavity; connecting a bypass exhaust conduit between the firstcavity in the main chamber and the second cavity in the middle chamberfor providing an unrestricted flow of residual etchant gas from thesecond cavity after an etching process; conducting an etching process ona wafer in the main chamber; and evacuating residual etchant gas fromthe second cavity through the apertured opening and the bypass exhaustconduit by a pump means.

[0021] The method for preventing corrosion in an etch chamber byresidual etchant gas may further include the step of evacuating residualetchant gas from the second cavity by a turbo pump, or the step ofmounting a gate valve between the second cavity and the pump means. Themethod may further include the step of providing the wafer platform inan electrostatic chuck, or the step of positioning a wafer on the waferplatform for carrying out an etching process. The method may furtherinclude the step of providing the apertured opening in a shower head fordispersing an etchant gas plasma into the first cavity for etching awafer. The method may further include the step of evacuating more thanhalf of the residual etchant gas from the second cavity through thebypass exhaust conduit. The method may further include the step ofevacuating more than ¾ of the residual etchant gas from the secondcavity through the bypass exhaust conduit. The method may furtherinclude the step of providing the metal sidewall in aluminum, or thestep of igniting the plasma in the etchant gas flown into the secondcavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] These and other objects, features and advantages of the presentinvention will become apparent from the following detailed descriptionand the appended drawings in which:

[0023]FIG. 1 is a graph illustrating a conventional transformer-coupledplasma etch chamber including a middle chamber and a main chamber.

[0024]FIG. 2 is a graph illustrating a present inventiontransformer-coupled plasma etch chamber that is equipped with a bypassexhaust conduit for preventing corrosion in the middle chamber byresidual etchant gas.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0025] The present invention discloses an apparatus and a method forpreventing etch chamber contamination caused by corrosion in the middlechamber wall by residual etchant gas due to poor evacuation through anapertured opening connecting the middle chamber and the main chamber.

[0026] In the novel apparatus, a bypass exhaust conduit is added to theetch chamber providing fluid communication between a cavity in themiddle chamber and a cavity in the main chamber such that when a pumpmeans is used to evacuate the main chamber cavity, residual etchant gasin the middle chamber cavity can be rapidly exhausted out of the middlechamber. The metal sidewall in the middle chamber can thus be preventedfrom being etched by the residual etchant gas after an etching processis completed on a wafer in the main chamber. A potential particlecontamination problem caused by the etched metal surface is thusavoided.

[0027] In a typical etching process for a metallization layer on an ICdevice, for instance, for a metallization layer formed of aluminum oraluminum alloys with copper, tungsten, etc an etchant gas of Cl₂ orBCl₃, and more likely a mixture of Cl₂ and BCl₃ is used. The mix ratioof the etchant gasses can be suitably controlled by their individualflow rate into the etch chamber. For instance, for etching aluminum, asuitable mix ratio of Cl₂: BCl₃ may be between 0.5:1 and 4:1. A suitableflow rate for the gases is usually between 100 Sccm and 500 Sccm, whichpresents a chamber pressure between 5 mTorr and 25 mTorr. For certainapplications in etching metallization layers, i.e. specifically in theetching of via or contact holes, another etchant gas of polymeric naturesuch as CHF₃ or CF₄ may also be used such that sidewall passivation maybe formed of the polymeric material to further enhance anisotropic etcheffect, i.e. a more vertical aluminum sidewall after etching can beobtained. A preferred mixed ratio of Cl₂ and BCl₃ is between 2:1 and4:1.

[0028] In the high plasma density reactor shown in FIG. 2, of thetransformer-coupled type, a desirable aluminum etch rate can be obtainedby suitably adjusting the mix ratio of Cl₂ and BCl₃ For instance, whenan eight inch wafer is positioned on an electrostatic chuck forconducting an etching process, a mix ratio of 4:1 of Cl₂:BCl₃ can besuitably used to achieve a total flow rate of 300 Sccm and a chamberpressure of about 20 mTorr. Under such etch conditions, a desirable etchrate between 10,000 Å/min and 13,000 ÅA/min can be achieved.

[0029] Referring now to FIG. 2, wherein an illustration of the presentinvention transformer-coupled plasma etch chamber 30 is shown. Theplasma etch chamber 50 is constructed of a middle chamber 20 situatedinside a main chamber 32 with the middle chamber 20 suspended over anelectrostatic chuck 26 for holding a wafer 30 thereon. The middlechamber is constructed by a top ceramic plate 12, a bottom ceramic plate16 and a metal sidewall 22. A gas inlet 14 is provided at a center ofthe top ceramic plate 12 for flowing in either an etchant gas mixture oran inert purge gas. A shower head 18 is provided at the center of thebottom ceramic plate 16 which is provided with small diameter openingsfor dispersing an etchant gas plasma into the chamber cavity 28 of themain chamber 32. A first electrode in the form of a RF coil 52 ispositioned over the middle chamber 20 which works in combination with asecond electrode 54 connected to the electrostatic chuck 26 for ignitinga plasma in the etchant gas mixture within cavity 24 in the middlechamber 20.

[0030] After an etching process has been conducted on wafer 30positioned on top of the electrostatic chuck 26, and the wafer 30 issubsequently removed, the cavity 28 of the main chamber 32 is evacuatedby a turbo pump 34 through a gate valve 36. Typically, a high flow rateturbo pump 34 is used for providing high flow rates at very low chamberpressures. For instance, in one configuration, the turbo pump 34 iscapable of pumping about 50 Sccm at a low pressure of about 1 mTorr, andat a substantially higher rate such as 300 Sccm at a higher pressure ofabout 4 mTorr. When the chamber pressure is significantly higher, i.e.higher than 200 mTorr, the turbo pump cannot be used for fear of damagesto the pump. Under a high chamber pressure condition, the flow controlvalve 42 for the turbo pump 34 can be closed while the flow controlvalve 44 can be opened to evacuate cavity 28 in the main chamber 32 bythe dry pump 38 directly.

[0031] The present invention novel bypass exhaust conduit 60, as shownin FIG. 2, is connected to the cavity 24 in the middle chamber 20 atopening 40 and to the cavity 28 of the main chamber 32 at opening 46.The direct connection between the middle chamber cavity and the mainchamber cavity allows a rapid evacuation of any residual etchant gasleft in the middle chamber cavity while the main chamber cavity isevacuated by either the turbo pump 34 or the dry pump 38. The rapidevacuation can be effectively used to empty the middle chamber cavitysuch that no etchant gas is left behind to corrode the metallic sidewall22 which is frequently made of aluminum. Any potential particlecontamination problem caused by the metal corrosion can thus be avoided.The bypass exhaust conduit 60 of the present invention can be controlledby a control valve 62 positioned at near the opening 40 to the middlechamber cavity 24.

[0032] The present invention novel apparatus and method for preventingan etch chamber from particle contamination caused by corrosion of ametal sidewall in a middle chamber by residual etchant gas has thereforebeen amply described in the above description and in the appendeddrawing of FIG. 2.

[0033] While the present invention has been described in an illustrativemanner, it should be understood that the terminology used is intended tobe in a nature of words of description rather than of limitation.

[0034] Furthermore, while the present invention has been described interms of a preferred and alternate embodiment, it is to be appreciatedthat those skilled in the art will readily apply these teachings toother possible variations of the inventions.

[0035] The embodiment of the invention in which an exclusive property orprivilege is claimed are defined as follows.

1. A plasma etch chamber comprising: a main chamber having a firstcavity, a wafer platform and a spent etchant gas outlet in fluidcommunication with a pump means for exhausting a spent etchant gas; amiddle chamber having a second cavity therein situated inside said firstcavity and suspended over said wafer platform; said middle chamber beingformed by a top ceramic plate, a bottom ceramic plate and a metalsidewall; said second cavity being in fluid communication with saidfirst cavity through an apertured opening situated in said bottomceramic plate for feeding an etchant gas plasma into said first cavity,said second cavity being in fluid communication with an etchant gassource through an etchant gas inlet situated in said top ceramic plate;and a bypass conduit providing fluid communication between said secondcavity in said middle chamber through an opening in said top ceramicplate and said first cavity in said main chamber such that any residualetchant gas in said second cavity is evaluated by said pump meansthrough said first cavity without causing corrosion in said metalsidewall of said middle chamber.
 2. A plasma etch chamber according toclaim 1, wherein said first cavity in said main chamber has a volumethat is at least twice the volume of said second cavity in said middlechamber.
 3. A plasma etch chamber according to claim 1, wherein saidwafer platform is an electrostatic chuck.
 4. A plasma etch chamberaccording to claim 1, wherein said apertured opening in said bottomceramic plate is a shower head for dispersing an etchant gas plasma intosaid first cavity of said main chamber.
 5. A plasma etch chamberaccording to claim 1, wherein said bypass exhaust conduit allows saidresidual etchant gas to flow therethrough at a flow rate at least twicethe flow rate of said residual etchant gas flown through said aperturedopening in said bottom ceramic plate.
 6. A plasma etch chamber accordingto claim 1, wherein said spent etchant gas outlet being in fluidcommunication with a turbo pump.
 7. A plasma etch chamber according toclaim 1, wherein said spent etchant gas outlet being in fluidcommunication with a pump through a gate valve for controlling apassageway of said spent etchant gas.
 8. A plasma etch chamber accordingto claim 1, wherein said top ceramic plate, and said bottom ceramicplate being formed of a ceramic material that is resistant to saidetchant gas plasma.
 9. A plasma etch chamber according to claim 1,wherein said metal sidewall of said middle chamber being formed ofaluminum.
 10. A plasma etch chamber according to claim 1, wherein saidetchant gas plasma being formed of at least one gas selected from thegroup consisting of Cl₂ and BCl₃ in said middle chamber by a radiofrequency coil.
 11. A method for preventing corrosion in an etch chamberby residual etchant gas comprising the steps of: providing an etchchamber comprising a main chamber and a middle chamber, said mainchamber further comprises a first cavity and a wafer platform with saidmiddle chamber suspended over said wafer platform, said middle chamberfurther comprises a top ceramic plate having an etchant gas inlettherethrough, a bottom ceramic plate having an apertured opening forpassing an etchant gas plasma therethrough and a metal sidewall defininga second cavity; connecting a bypass exhaust conduit between said firstcavity in said main chamber and said second cavity in said middlechamber for providing an unrestricted flow of residual etchant gas fromsaid second cavity after the completion of an etching process; andconducting an etching process on a wafer in said main chamber; andevacuating residual etchant gas from said second cavity through saidapertured opening and said bypass exhaust conduct by a pump means.
 12. Amethod for preventing corrosion in an etch chamber by residual etchantgas according to claim 11 further comprising the step of evacuatingresidual etchant gas from said second cavity by a turbo pump.
 13. Amethod for preventing corrosion in an etch chamber by residual etchantgas according to claim 11 further comprising the step of mounting a gatevalve between said second cavity and said pump means.
 14. A method forpreventing corrosion in an etch chamber by residual etchant gasaccording to claim 11 further comprising the step of providing saidwafer platform in an electrostatic chuck.
 15. A method for preventingcorrosion in an etch chamber by residual etchant gas according to claim11 further comprising the step of positioning a wafer on said waferplatform for carrying out an etching process.
 16. A method forpreventing corrosion in an etch chamber by residual etchant gasaccording to claim 11 further comprising the step of providing saidapertured opening in a shower head for dispersing an etchant gas plasmainto said first cavity for etching a wafer.
 17. A method for preventingcorrosion in an etch chamber by residual etchant gas according to claim111 further comprising the step of evacuating more than half of theresidual etchant gas from said second cavity through said bypass exhaustconduit.
 18. A method for preventing corrosion in an etch chamber byresidual etchant gas according to claim 11 further comprising the stepof evacuating more than ¾ of the residual etchant gas from said secondcavity through said bypass conduit.
 19. A method for preventingcorrosion in an etch chamber by residual etchant gas according to claim11 further comprising the step of providing said metal sidewall inaluminum.
 20. A method for preventing corrosion in an etch chamber byresidual etchant gas according to claim 11 further comprising the stepof igniting a plasma in said etchant gas flown into said second cavity.